60 THE STORY OF FISH LIFE. 



that other fishes, upon which it preys, approach 

 near enough to be seized before they are aware of 

 its presence. Sometimes the fishing-frog will 

 bury itself in the mud, leaving only the "flags" 

 exposed. By skilfully waving these, fish are 

 attracted and suddenly engulfed. 



The dorsal fin in the sea-horse (Hippocarripus) 

 is quite peculiar, being used as a propeller, its 

 vigorous movement serving to drive the fish 

 through the water in its characteristic upright 

 (vertical) position. The tail or caudal fin is 

 absent. The tail itself is used as an organ of 

 prehension. 



If we were to examine the skeleton of one of 

 the median fins, we should find that every one of 

 the supporting columns or fin-rays was attached 

 at its base to a second pointed rod or spike, which, 

 in turn, projecting downwards among the muscles 

 of the body, became attached to yet another 

 spine which grew upwards from the vertebral 

 column. 



The caudal or tail-fin we have already studied 

 in discussing the tail proper. We need only 

 say here that, like the dorsal fins, it is made up 

 of stiff fin-rays supporting a thin membrane. 

 But there is one point which has not yet been 

 noticed, and that is, its position. In the fish 

 then it is vertical. There is nothing wonderful in 

 this someone will remark. But wait; compare 

 it with the caudal fin of the porpoise or the 

 whale. It will then be seen that its vertical 

 position after all has probably a lesson to teach. 

 In the whale or the porpoise the tail - fin is 7iot 

 vertical but horizontal in position. Why is this ? 



